The present invention relates to an aromatic diazonium salt, a radiation sensitive composition containing the aromatic diazonium salt and a method for forming a pattern using the radiation sensitive composition. More particularly, it relates to a method for forming a pattern which is especially suitable for production of, for example, various electronic parts such as semiconductor devices, a radiation sensitive composition used for this method and an aromatic diazonium salt contained in this radiation sensitive composition.
Hitherto, photosensitive compositions or photolithographic techniques suitable for production of electronic parts such as semiconductor devices have been proposed, for example, in Japanese Patent Kokai Nos. 60-238829, 63-13035 and 59-45439. Further, diazonium salts or photosensitive compositions containing the diazonium salts have been proposed, for example, in Japanese Patent Kokai Nos. 51-93998 and 61-219038.
The above Japanese Patent Kokai No. 60-238829 shows a method which comprises providing a photosensitive film containing a photosensitive diazonium salt on a photoresist film and then carrying out pattern exposure using a light to which both the photoresist and the photosensitive diazonium salt are sensitive in order to form a very fine pattern with high resolution and to obtain an image of high contrast without reducing the sensitivity of the photoresist so much. The photosensitive film containing the photosensitive diazonium salt is considerably low in transmittance before exposure, but shows such photobleaching properties as the film becomes gradually transparent upon exposure. Therefore, when the photosensitive film is exposed to aerial image of mask, the aerial image undergoes rapid bleaching in light portion and undergoes slow bleaching in dark portion. Therefore, by utilizing such bleaching property with light, difference in exposure of photoresist in the light portion and the dark portion is greater than when the above photosensitive film is not present and thus contrast is improved.
The method disclosed in the above-mentioned Japanese Patent Kokai No. 63-13035 comprises forming an alkali-soluble polymer film on a substrate, further forming thereon a radiation sensitive composition layer containing a diazonium salt to produce a two-layer film and then forming a pattern by exposure and development in order to obtain a pattern of film having dry etching durability and high sensitivity and contrast. According to this method, a radiation-induced chemical reaction takes place at interface between these two layers and hence insolubilization markedly progresses at the two-layer interface to increase difference in solubility in developing solution between exposed area and unexposed area, thereby to obtain high contrast.
Japanese Patent Kokai No. 59-45439 relates to a radiation sensitive composition of high sensitivity and discloses a radiation sensitive composition containing a polymer which is unstable in acid and a polymerization initiator which produces acid when exposed to radiation. This composition has high sensitivity owing to acid-catalyzed amplification reaction.
Further, Japanese Patent Kokai No. 51-93998 cited above discloses a curable photosensitive composition comprising a diazonium salt and an epoxy compound.
These conventional techniques did not give consideration to the many problems which occur in production of very fine electronic parts such as LSI devices. That is, as mentioned, for example, in the above Japanese Patent Kokai No. 60-238829, diazonium salts hitherto used have halogen ion or anion produced from halogen compounds of boron, aluminum, iron, zinc, arsenic, antimony or phosphorus. These metals or semimetals cause defects in LSI devices. Further, the above Japanese Patent Kokai No. 63-13085 mentions diazonium salts containing neither metals nor semimetals, such as diazonium salt of sulfonic acid, but there is a step of using metal ions such as sodium in the course of synthesis. They also suffer from the above problems due to a slight amount of unremovable metal impurities.